Invert Emulsion Drilling Fluids with Fatty Acid and Fatty Amine Rheology Modifiers

ABSTRACT

Provided here are various invert emulsion drilling fluid compositions. One such invert emulsion drilling fluid is a water in oil emulsion, which can include an invert emulsifier to stabilize the water in oil emulsion, a fatty acid, a 36 carbon fatty dimer diamine, a filtration control agent; and an inorganic mineral including one or more of lime, calcium chloride, and barite. The invert emulsion drilling fluids can be formulated to be substantially free of clay.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of and the priority to the U.S.Provisional Application No. 62/428,361 filed on Nov. 30, 2016.

FIELD

The disclosure relates to drilling fluids for oil and gas exploration.More specifically, the disclosure relates to the composition and use ofinvert emulsion fluids as rheology modifiers.

BACKGROUND

A conventional invert emulsion fluid for drilling in oil and gasexploration generally includes clay in the formulation, where the clayacts as the primary rheology (viscosity) modifier. The clay can beorganophilic clay or organoclay. Drilling fluids formulated with anorganophilic clay can have a degradation of rheology properties overtime. In other words, the organophilic clay formulated fluids can have aloss of viscosity over time, owing to the inability of the clay tomaintain a necessary level of viscosity. One solution to the loss ofviscosity with time is to add an excess amount of an organophilic clayto the drilling fluid, or to add an excess of low gravity solids (LGS)to the drilling fluid, or both. However, adding excess clay, or LGS, orboth can increase the cost of drilling and can severely impact otherimportant drilling fluid properties. These impacts on cost, or fluidproperty, or both can necessitate further costly treatments downhole orto the drilling fluid as remedies. For example, the addition of excessLGS can increase the plastic viscosity and the solids volume percentage,which can impact the rate of penetration of a drill bit into aformation, thus increasing the cost of drilling.

Drilling fluid rheology can change with increasing well depth as aresult of changes in pressure and temperature. Such changes can causechanges in the equivalent circulating density (ECD) while drillingadvances down through a formation. These fluctuations in ECD can lead tofracture of the formation when operating in a narrow window of porepressure and fracture gradient. This can lead to formation damage andmud losses, thus increasing drilling costs. The use of thinner fluids tominimize rheology fluctuations, in general, can lead to lesser ECD;however, the fluid rheology may need to be such that the fluidproperties enable cuttings removal and help to suspend drill solids.There are competing needs of greater viscosity for cuttings removal andsuspension of solids versus lesser viscosity for better ECD.

SUMMARY

A need has been recognized for an invert emulsion drilling fluid withimproved rheology and with stability of rheology during drilling tobalance the needs of better ECD with cuttings removal and solidssuspension. Certain embodiments relate to invert emulsion drilling fluidcompositions and methods of drilling a wellbore in a formation using theinvert emulsion drilling fluid compositions. In various embodiments, aninvert emulsion drilling fluid can include a water in oil emulsion; aninvert emulsifier to stabilize the water in oil emulsion in an amountoperable to stabilize the water in oil emulsion; a fatty acid having atleast eight carbons and at least one carboxylic acid group; a 36 carbonfatty dimer diamine; a filtration control agent; and an inorganicmineral including one or more of lime, calcium chloride, and barite(barium sulfate, BaSO₄).

In various embodiments, the fatty acid can be a 36 carbon dimer diacidhaving the general formula illustrated by Formula 1.

In various embodiments, the 36 carbon fatty dimer diamine can have thegeneral formula illustrated by Formula 2.

In various embodiments, the fatty acid can be a mixture of C16 and C18saturated linear alpha carboxylic acids and can include a C18 fatty acidas illustrated by Formula 3.

In various embodiments, the fluid can be formulated to have an oil towater ratio from 5:95 to 95:5 by volume. In various embodiments, thefluid can be formulated to have a density of 63 to 164 lbm/ft³ (poundmass per cubic foot). In various embodiments, the fluid can beformulated without clay and without LGS. In various embodiments, thefluid can be formulated to have a calcium chloride (CaCl₂) water phasesalinity concentration of 200 to 390 thousand parts per million. Invarious embodiments, the fluid can be formulated to have 2 to 25 lbm/bbl(pound mass per barrel) of the invert emulsifier. In variousembodiments, the fluid can be formulated to have 0.5 to 5 lbm/bbl oflime. In various embodiments, the fluid can be formulated to have atleast 0.5 to 5 lbm/bbl of the 36 carbon dimer diacid. In variousembodiments, the fluid can be formulated to have 0.25 to 5 lbm/bbl ofthe filtration control agent. In various embodiments, the fluid can beformulated to have at least 0.25 lbm/bbl of the 36 carbon fatty dimerdiamine. In various embodiments, the oil can be selected from the groupconsisting of mineral oil, diesel fuel, and synthetic oil, andcombinations thereof. In various embodiments, the fluid can beformulated to have a yield point greater than 15 lbf/100 ft² (poundforce per hundred square feet). In various embodiments, the fluid can beformulated to have a low shear yield point greater than 7 lbf/100 ft².

In various embodiments, a method of drilling a wellbore with an invertemulsion fluid can comprise drilling in a formation using an invertemulsion fluid, wherein the fluid includes a water in oil emulsion; aninvert emulsifier to stabilize the water in oil emulsion in an amountoperable to stabilize the water in oil emulsion; a fatty acid having atleast eight carbons and at least one carboxylic acid group; a 36 carbonfatty dimer diamine; a filtration control agent; and an inorganicmineral including one or more of lime, calcium chloride, and barite. Invarious embodiments, the fatty acid can be a 36 carbon dimer diacidhaving the formula illustrated by Formula 1. In various embodiments, the36 carbon fatty dimer diamine can have the formula illustrated byFormula 2. In various embodiments, the fatty acid can have at leasteight carbons and at least one carboxylic acid group. In variousembodiments, the fatty acid can be a mixture of C16 and C18 saturatedlinear alpha carboxylic acids. In various embodiments, the fluid canhave an oil to water ratio from 5:95 to 95:5 by volume. In variousembodiments, the fluid can have a density of 63 to 164 lbm/ft³. Invarious embodiments, the fluid can have a CaCl₂ water phase salinityconcentration of 200 to 390 thousand parts per million. In variousembodiments, the fluid can have 2 to 25 lbm/bbl of the invertemulsifier. In various embodiments, the fluid can have 0.5 to 5 lbm/bblof lime. In various embodiments, the fluid can have at least 0.5 to 5lbm/bbl of the 36 carbon dimer diacid. In various embodiments, the fluidcan have 0.25 to 5 lbm/bbl of the filtration control agent. In variousembodiments, the fluid can have at least 0.25 lbm/bbl of the 36 carbonfatty dimer diamine. In various embodiments, the oil can be selectedfrom the group consisting of mineral oil, diesel fuel, and syntheticoil, and combinations thereof. In various embodiments, the fluid canhave a yield point greater than 15 lbf/100 ft². In various embodiments,the fluid can have a low shear yield point greater than 7 lbf/100 ft².

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be readily understood by the following detaileddescription in conjunction with the accompanying drawings. Embodimentsare illustrated by way of example and not by way of limitation in theaccompanying drawings.

FIG. 1 is a graphical representation of the plastic viscosity (PV), theyield point (YP), and the low shear yield point (LSYP) data of the fourfluids described in Table 1A, in accordance with various embodiments.

FIG. 2 is a graphical representation of PV, YP, and LSYP data of thefour fluids described in Table 2A, in accordance with variousembodiments.

FIG. 3 is a graphical representation of PV, YP, and LSYP data of thefour fluids described in Table 3A, in accordance with variousembodiments.

DETAILED DESCRIPTION

Embodiments of the present disclosure describe invert emulsion fluids(IEFs) for drilling in oil and gas exploration, where the fluids have acombination of fatty acid and fatty amine compounds for rheologymodification. In some embodiments, the fluids can be substantially freeof clay formulations. Further embodiments are described and disclosedhere.

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the various embodiments. Inother instances, well-known processes and methods may not been describedin particular detail in order not to unnecessarily obscure theembodiments described here. Additionally, illustrations of embodimentsmay omit certain features or details in order to not obscure theembodiments described here.

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, wherein like numeralsdesignate like parts throughout, and in which is shown by way ofillustration, embodiments in which the subject matter of the presentdisclosure can be practiced. Other embodiments can be utilized, andlogical changes can be made without departing from the scope of thepresent disclosure. Therefore, the following detailed description is notto be taken in a limiting sense.

The description may use the phrases “in some embodiments,” “in variousembodiments,” “in certain embodiment,” or “in embodiments,” which mayeach refer to one or more of the same or different embodiments.Furthermore, the terms “comprising,” “including,” “having,” and thelike, as used with respect to embodiments of the present disclosure, aresynonymous.

As used here, when an invert emulsion fluid is “substantially free of” acomponent, the amount of that component present in the composition issuch that it will not substantially impair the activity of the invertemulsion fluids and will confer advantages as described in a particularembodiment. For example, if an invert emulsion fluid is said to besubstantially free of clay, then the concentration of clay in the invertemulsion fluid, as determined by a statistically significantquantitative evaluation, would be less than 5%. The term “approximately”as used here means within an acceptable error range for the particularvalue as determined by one of ordinary skill in the art, which willdepend in part on how the value is measured or determined, i.e., thelimitations of the measurement system.

Various embodiments disclosed here can relate to formulations of invertemulsion fluids (IEFs) that are substantially free of organoclay andcontain rheology modifiers, including a combination of a fatty acid anda fatty amine. An absence of organoclay as a primary viscosifier in anIEF can result in a fluid with lesser plastic viscosity and with minimalimpact on ECD while providing greater rates of penetration into aformation. An absence of organoclay in a fluid can provide a flatterrheology to the fluid that can be essential for drilling deep wellswhere the temperature gradient is large. An advantage of variousembodiments disclosed here may be that a small concentration of both adimer fatty diacid and a dimer fatty diamine may provide greater low-endrheology as compared to when the dimer fatty diacid or the dimer fattydiamine are used alone as rheology modifiers in an invert emulsionfluid. A further advantage of various embodiments disclosed here is thatthese rheology modifier combinations can provide good low-end rheology,thus resulting in reduced barite sag and good hole-cleaning capability.A further advantage of various embodiments disclosed is that the effectof contamination on rheology of IEFs that are substantially free oforganoclay may be minimal, and any effect of contamination may be easilytreated by drilling fluid conditioners.

Without being bound by theory, the fatty acid and fatty amine mayprovide a synergistic effect that may provide enhanced low-end rheologyproperties to IEFs that are substantially free of organoclay, thusincreasing hole-cleaning capacity and barite sag resistance of thefluid. This combination of rheology modifiers also can be used inconventional oil-based drilling fluids formulated with an organoclay. Insome embodiments, examples of fatty acids can include C32-C36 dimerfatty diacids and C16-C18 fatty acids. In some embodiments, an exampleof a fatty amine can include a C32-C36 dimer fatty diamine.

Selective rheological properties of an IEF can be predictive as to howthe IEF can perform for drilling purposes. These properties include PV,YP, and yield stress. For drilling purposes, PV can be indicative ofdrilling speed where a lesser PV indicates an ability to drill faster,YP can be indicative of the cuttings carrying capacity of an IEF throughan annulus (the hole cleaning ability of the IEF) where a greater YPimplies a non-Newtonian fluid with better ability to carry away cuttingscompared to a fluid of similar density, and yield stress can provide anindication of the susceptibility of an IEF to barite sag where a greatervalue generally provides better resistance.

The YP and PV properties can be evaluated using the Bingham plastic (BP)rheology model. YP can be determined by extrapolating the BP model to ashear rate of zero and can represent the stress required to move thefluid. YP can be expressed in the units of lbf/100 ft². Generally, YPvalues greater than approximately 15 lbf/100 ft² can be considered asuitable threshold for drilling purposes for providing suitable abilityto carry away cuttings. PV can represent the viscosity of a fluid whenextrapolated to infinite shear rate and can be expressed in units ofcentipoise (cP). PV can indicate the type and concentration of thesolids in an IEF, and a lesser PV generally is preferred for aformulation of an IEF as a lesser PV indicates a faster potentialdrilling rate. Both PV and YP can be calculated using 300 revolutionsper minute (rpm) and 600 rpm shear rate readings on a standard oilfieldviscometer and can be calculated by Equations 1 and 2.

PV=600 rpm reading−300 rpm reading  [Equation 1]

YP=300 rpm reading−PV  [Equation 2]

Regarding yield stress, a value for yield stress can be indicated by theparameter τ₀ (Tau-zero), which is a parameter from the Herschel Buckley(HB) rheology model. Generally, an IEF with a relatively large yieldstress value can be expected to provide a better sag resistance, whichis desirable for drilling purposes. The parameter τ₀ can be determinedby fitting the HB model to a shear stress versus shear rate curve, whichcan be the dial readings plotted against the corresponding rpmdetermined on a standard oilfield viscometer. τ₀ can be expressed insimilar units as YP. τ₀ can be estimated within reasonable engineeringtolerances by calculating a LSYP value using Equation 3.

LSYP=2*(300 rpm reading)−600 rpm reading  [Equation 3]

An LSYP value equal to or greater than approximately 7 lbf/100 ft² canbe considered an acceptable threshold value for drilling purposes forminimizing barite sag.

Embodiments provided in this disclosure relate to an invert emulsiondrilling fluid. In some embodiments, the fluid can contain a water inoil emulsion, an invert emulsifier to stabilize the water in oilemulsion, a carbon 36 dimer diacid having the formula illustrated byFormula 1, a 36 carbon fatty dimer diamine having the formulaillustrated by Formula 2, a filtration control agent; and an inorganicmineral including one or more of lime, calcium chloride, and barite.

In various embodiments, the fluid can be formulated without clay. Invarious embodiments, the fluid can be formulated without organoclay. Invarious embodiments, the fluid can be formulated without LGS.

In various embodiments, the 36 carbon dimer diacid component can includeother fatty diacids of lesser chain length, such as a C34, or greaterchain length, such as a C38, or combinations of these fatty acids. Invarious embodiments, the 36 carbon dimer diacid can have a carbon tocarbon linkage between the C9 and the C10 of dimers. In variousembodiments, the 36 carbon dimer diacid can have a carbon to carbonlinkage between the other locations with the range of C8 to C12 ofdimers.

In various embodiments, the fluid can be formulated to be approximately90 lbm/ft³. In various embodiments, the fluid can be formulated to havefrom 63 to 134 lbm/ft³.

In various embodiments, the fluid can be formulated to have an oil towater ratio of approximately 5 to 95 to approximately 95 to 5. Invarious embodiments, the fluid can be formulated to have an oil to waterratio of approximately 5 to 95 to approximately 50 to 50.

In various embodiments, the fluid can be formulated to have a CaCl₂water phase salinity concentration of approximately 250 thousand partsper million. In various embodiments, the fluid can be formulated to havea CaCl₂ water phase salinity concentration of approximately 100 to 390thousand parts per million.

In various embodiments, the fluid can be formulated to haveapproximately 10 lbm/bbl of the invert emulsifier. In variousembodiments, the fluid can be formulated to have approximately 5 to 25lbm/bbl of the invert emulsifier. In various embodiments, the invertemulsifier can be any suitable invert emulsifier for formulatingdrilling fluids.

In various embodiments, the fluid can be formulated to haveapproximately 1.5 lbm/bbl of lime. In various embodiments, the fluid canbe formulated to have approximately 0.5 to 5 lbm/bbl of lime.

In various embodiments, the fluid can be formulated to have at leastapproximately 0.25 lbm/bbl of the 36 carbon dimer diacid. In variousembodiments, the fluid can be formulated to have at least approximately0.25-10 lbm/bbl of the 36 carbon dimer diacid. The concentration of the36 carbon dimer diacid can be lesser or greater than this range,depending on mud weight.

In various embodiments, the fluid can be formulated to haveapproximately 2 lbm/bbl of the filtration control agent. In variousembodiments, the fluid can be formulated to have approximately 1-10lbm/bbl of the filtration control agent. In various embodiments, thefiltration control agent can be an ADAPTA® filtration control agent,available from Halliburton Company, headquartered in Houston, Tex., USA.In various embodiments, the filtration control agent can be any suitablefiltration control agent for formulating drilling fluids.

In various embodiments, the fluid can be formulated to haveapproximately 28-32 lbm/bbl of calcium chloride. In various embodiments,the fluid can be formulated to have approximately 83-87 lbm/bbl ofwater. The concentration of calcium chloride and water can vary outsidethese ranges, depending on additives to the mud and the mud weight.

In various embodiments, the fluid can be formulated to have at leastapproximately 0.25 lbm/bbl of the 36 carbon fatty dimer diamine. Invarious embodiments, the fluid can be formulated to have approximately0.25 to 10 lbm/bbl of the 36 carbon fatty dimer diamine.

In various embodiments, the oil can be selected from the groupconsisting of mineral oil, diesel fuel, and synthetic oil, andcombinations thereof.

In various embodiments, the fluid can be formulated to haveapproximately 220-225 lbm/bbl of barite. The concentration of barite candepend on the oil to water ratio and mud weight and can be outside thisrange.

In various embodiments, the fluid can be formulated to have a yieldpoint greater than approximately 15 lbf/100 ft².

In various embodiments, the fluid can be formulated to have a low shearyield point greater than approximately 7 lbf/100 ft².

In various embodiments, an invert emulsion drilling fluid can beformulated to include a water in oil emulsion with a ratio of oil towater of approximately 70 to 30, an invert emulsifier to stabilize thewater in oil emulsion, a 16 to 18 carbon carboxylic acid, wherein the 16to 18 carbon carboxylic acid includes an 18 carbon carboxylic acidhaving the formula illustrated by Formula 3, a 36 carbon fatty dimerdiamine having the formula illustrated by Formula 2, a filtrationcontrol agent, and an inorganic mineral including one or more of lime,calcium chloride, and barite.

In various embodiments, the fluid can be substantially free of clay. Invarious embodiments, the fluid can be substantially free of low gravitysolids.

In various embodiments, the fluid can be formulated to be approximately90 lbm/ft³. In various embodiments, the fluid can be formulated to havefrom 63 to 134 lbm/ft³.

In various embodiments, the fluid can be formulated to have an oil towater ratio of approximately 95 to 5 to approximately 5 to 95.

In various embodiments, the fluid can be formulated to have a CaCl₂water phase salinity concentration of approximately 250 thousand partsper million. In various embodiments, the fluid can be formulated to havea CaCl₂ water phase salinity concentration of approximately 200 to 390thousand parts per million.

In various embodiments, the fluid can be formulated to haveapproximately 10 lbm/bbl of the invert emulsifier. In variousembodiments, the fluid can be formulated to have approximately 2 to 25lbm/bbl of the invert emulsifier. In various embodiments, the invertemulsifier can be any type of operable invert emulsifier. By way ofexample and not limitation, types of invert emulsifiers can includepolyamides, sulfates, sulfonates, and carboxylates withhydrophile-lipophile balance value of less than 11. In variousembodiments, the invert emulsifier can be any suitable invert emulsifierfor formulating drilling fluids.

In various embodiments, the fluid can be formulated to haveapproximately 1.5 lbm/bbl of lime. In various embodiments, the fluid canbe formulated to have approximately 1 to 3 lbm/bbl of lime.

In various embodiments, the fluid can be formulated to have at leastapproximately 3 lbm/bbl of the 16 to 18 carbon carboxylic acid. Invarious embodiments, the fluid can be formulated to have at leastapproximately 1.5 to 5 lbm/bbl of the 16 to 18 carbon carboxylic acid.

In various embodiments, the fluid can be formulated to haveapproximately 2 lbm/bbl of the filtration control agent. In variousembodiments, the fluid can be formulated to have approximately 1-3lbm/bbl of the filtration control agent. In various embodiments, thefiltration control agent can be ADAPTA® filtration control agent. Invarious embodiments, the filtration control agent can be any suitablefiltration control agent for formulating drilling fluids.

In various embodiments, the fluid can be formulated to haveapproximately 28-32 lbm/bbl of calcium chloride. In various embodiments,the fluid can be formulated to have approximately 83-87 lbm/bbl ofwater.

In various embodiments, the fluid can be formulated to have at leastapproximately 1.5 lbm/bbl of the 36 carbon fatty dimer diamine. Invarious embodiments, the fluid can be formulated to have approximately 1to 3 lbm/bbl of the 36 carbon fatty dimer diamine.

In various embodiments, the oil can be selected from the groupconsisting of mineral oil, diesel fuel, and synthetic oil, andcombinations thereof.

In various embodiments, the fluid can be formulated to haveapproximately 220-225 lbm/bbl of barite.

In various embodiments, the fluid can be formulated to have a yieldpoint greater than approximately 15 lbf/100 ft². In various embodiments,the fluid can be formulated to have a low shear yield point greater thanapproximately 7 lbf/100 ft².

Examples

The present disclosure describes compositions for invert emulsion fluids(IEFs) with fatty acid and fatty amine rheology modifiers as illustratedand described here in the examples.

In the various examples provided here, selected IEFs that aresubstantially free of organoclay were formulated. The fluids wereformulated to be 90 pounds per cubic foot (pcf) fluids with an oil towater ratio (OWR) of 70:30 and a CaCl₂ water phase salinity (WPS)concentration of 250 thousand parts per million (Kppm).

In a first set of examples, a C36 fatty dimer diacid was used alone informulations as a rheology modifier to provide a baseline of performanceof IEF's without the combination of rheological modifiers, as disclosedand described here for various embodiments and examples. The C36 fattydimer diacid was used to formulate various 90 pcf IEFs that aresubstantially free of organoclay and has the chemical structure shown inFormula 1.

Table 1A provides formulation data for four IEFs with different amountsof Formula 1. No C36 fatty dimer diamine was added to these four IEFs.The formulations are labeled as Fluids 1-4. For each formulation, 150.3barrels of a mineral oil (available from Safra Company Limited,headquartered in Jeddah, Saudi Arabia) was added to a mixing tank. Tothe mineral oil an invert emulsifier (LE SUPERMUL™, available fromHalliburton Company, headquartered in Houston, Tex., USA) was added inan amount of 10 pounds per barrel (ppb), followed by mixing for 5minutes. Lime was added to this mixture in an amount of 1.5 ppb,followed by mixing for 5 minutes. Varying amounts of Formula 1 wereadded to this mixture, followed by mixing for 5 minutes. The amounts ofFormula 1 for Fluids 1-4 were 1.5 ppb, 3 ppb, 5 ppb, and 7 ppb,respectively. A filtration control agent (ADAPTA®) was added to thismixture in an amount of 2 ppb, followed by mixing for 5 minutes. Thefiltration control agent is a cross-linked methylstyrene/acrylatecopolymer and is to control fluid loss while minimizing impacts onplastic viscosity. Calcium chloride was added to this mixture in anamount of 29.6 ppb and water in an amount of 85.3 ppb, followed bymixing for 5 minutes. Barite was added to this mixture in an amount of223.7 ppb, followed by mixing for 10 minutes. Each formulation was hotrolled (placed in a pressurized high temperature and pressure cell androlled at 250° F. for 16 hours after all components were added to theformulation).

TABLE 1A Mixing Time Fluid after formulation component addition in orderof addition (min) Fluid 1 Fluid 2 Fluid 3 Fluid 4 Safra oil (bbl) —150.3 150.3 150.3 150.3 Emulsifier (ppb) 5 10 10 10 10 (LE SUPERMUL ™)LIME (ppb) 5 1.5 1.5 1.5 1.5 Rheology Agent—C36 5 1.5 3 5 7 fatty dimerdiacid (ppb) Filtration Control Agent 5 2 2 2 2 (ppb) (ADAPTA ®) CaCl₂(ppb) 5 29.6 29.6 29.6 29.6 Water (ppb) 85.3 85.3 85.3 85.3 Barite (ppb)10 223.7 222.7 220.7 220.7 Rheology Agent—C36 — 0 0 0 0 fatty dimerdiamine (ppb)

Each of the four IEFs of Table 1A were tested in a standard oilfieldviscometer at 3, 6, 100, 200, 300, and 600 rpm, and further were testedfor gel strength and High Temperature High Pressure (HTHP) fluid loss.An example of a standard oilfield viscometer can include a FANN® Model35 Viscometer, available from Fann Instrument Company, headquartered inHouston, Tex., USA. The rheology of the drilling fluid formulations wasmeasured according to American Petroleum Institute (API) RecommendedPractice 13B-2 (RP 13B-2) Section 6.3, Recommended Practice for FieldTesting of Oil-based Drilling Fluids. A sample of each of drillingfluids was placed in a thermostatically controlled viscometer cup. Anempty volume of approximately 100 cubic centimeter (cm³) was left in thecup to account for the displacement of the fluid due to the viscometerbob and sleeve. Measurements were made with minimum delay from the timeof preparation of the drilling fluid sample. Tests were carried out ateither 50±1° C. (120±1° F.). The temperature of the sample was monitoredand intermittent or constant shear at 600 rpm was used to stir thesample and obtain a uniform sample temperature. With the sleeve rotatingat 600 rpm, the viscometer dial reading was allowed to reach a steadyvalue and the required time to reach steady value depends on thecharacteristics of the drilling fluid sample. The dial reading of theviscometer at 600 rpm was recorded. The rotor speed was reduced to 300rpm. The viscometer dial reading was allowed to reach a steady value andthe dial reading at 300 rpm was recorded. The rotor speed wassubsequently reduced to 200 rpm, 100 rpm, 6 rpm, and 3 rpm, and at eachone of these foregoing rotational speeds, the viscometer dial readingwas allowed to reach a steady value and the dial readings at 200 rpm,100 rpm, 6 rpm, and 3 rpm were recorded. From the various measurementscollected during this test, PV, YP, and LSYP were calculated for thefour fluids and are shown in Table 1B.

The gel strength of the drilling fluids was also measured according tothe API RP 13B-2, Section 6.3. A sample of each of drilling fluids wasplaced in the viscometer for testing as described previously. Thedrilling fluid was stirred at 600 rpm for ten seconds and the drillingfluid sample was allowed to stand undisturbed for ten seconds. Thehand-wheel of the viscometer was turned slowly and steadily to produce apositive dial reading and the maximum reading thus obtained was recordedas the initial gel strength (10-second gel) in pound force per hundredsquare feet. The drilling fluid sample was restirred at 600 rpm for tenseconds and the drilling fluid sample was allowed to stand undisturbedfor ten minutes. The measurements were repeated as described in thisparagraph for the initial gel strength. The maximum reading now obtainedwas recorded as the ten-minute gel strength in pound force per hundredsquare feet. The gel strengths for the four drilling fluids are shown inTable 1B.

The HTHP fluid loss was measured according to the API RP 13B-2, Section7.2. The HTHP fluid loss test measures static filtration behavior ofdrilling fluid at elevated temperatures, such as 250° F. This test wasconducted using a HTHP filter press unit containing a filter cell, apressurized gas source, a heating system, a high-pressure filtratecollection vessel (maintained at proper back-pressure), and a filtermedium. The drilling fluid sample was stirred for five minutes using afield mixer and then poured into the filter cell, leaving at least 2.5centimeters of space in the cell to allow for fluid expansion. Thefilter paper was installed in the cell and the filter cell was assembledwith both top and bottom valves closed. The filter cell was placedinside the HTHP filter press unit with appropriate connections to thehigh-pressure filtrate collection vessel and the regulated pressurizedgas source. The temperature of the drilling fluid sample inside thefilter cell was maintained at the test temperature of 250° F. A pressureof about 100 pounds per square inch (psi) was maintained until the testtemperature of 250° F. was reached. Then, the pressure of the drillingfluid sample inside the filter cell was increased to the test pressureof 500 psi and the timer for the filtration process was started. Thefiltrate was collected in the filtrate collection vessel for thirtyminutes, and the volume of the filtrate was measured in milliliters (mL)using a graduated cylinder. The filtrate volume should be corrected to afilter area of 45.8 square centimeters (cm²). HTHP filter cells usuallyhave half the standard filter area or 22.58 cm², thus the observedvolume is usually doubled and reported. The HTHP fluid loss measurementsusing this test for the four drilling fluids are shown in Table 1B.

TABLE 1B Test Fluid 1 Fluid 2 Fluid 3 Fluid 4 600 rpm (cP) 36 45 40 38300 rpm (cP) 23 29 26 27 200 rpm (cP) 19 21 19 21 100 rpm (cP) 13 13.513 16  6 rpm (cP) 4 3 4 7  3 rpm (cP) 3 2 3 5 PV (cP ) 13 16 14 11 YP(lbf/100 ft²) 10 13 12 16 LSYP (lbf/100 ft²) 2 1 2 3 Gel Strength—10sec, 5.1 3 4.3 5 (lbf/100 ft²) Gel Strength—10 min, 3.6 3.3 4.7 4(lbf/100 ft²) HTHP fluid loss—250° F., 6 4 4 3 500 psi, 30 min (mL)

FIG. 1 graphically illustrates the plastic viscosity, the yield point,and the low shear yield point data of the four fluids of Table 1A. Ascan be seen in Table 1B and in FIG. 1, the YP and LSYP values remainrelatively flat with increasing amounts of C36 dimer diacid from 1.5 ppbto 7.0 ppb. This data indicates that C36 dimer diacid by itself does notappear to significantly impact the YP and LSYP values. Generally, for agood drilling fluid, LSYP value greater than or equal to 7 lbf/100 ft²is required, as noted previously. A larger LSYP value for the drillingfluid ensures good hole cleaning and greater barite sag resistance.Accordingly, Formula 1 by itself does not appear to impact the fluidrheology in a positive manner for drilling fluid purposes.

In a second set of examples, Formula 1 and a C36 fatty dimer diaminewere used as a rheology modifier combination to formulate four IEFs thatare substantially free of organoclay. The C36 fatty dimer diamine hasthe chemical structure shown in Formula 2.

Table 2A provides formulation data for four IEFs with different amountsof Formula 1 and Formula 2. The formulations are labeled as Fluids 1-4.For each formulation, 150.3 barrels of a mineral oil (available fromSafra Company Limited, headquartered in Jeddah, Saudi Arabia) was addedto a mixing tank. To the mineral oil an invert emulsifier (LE SUPERMUL™)was added in an amount of 10 ppb, followed by mixing for 5 minutes. Limewas added to this mixture in an amount of 1.5 ppb, followed by mixingfor 5 minutes. Varying amounts of Formula 1 were added to this mixture,followed by mixing for 5 minutes. The amounts of Formula 1 for Fluids1-4 were 1.5 ppb, 0, 1.5 ppb, and 1.5 ppb, respectively. A filtrationcontrol agent (ADAPTA®) was added to this mixture in an amount of 2 ppb,followed by mixing for 5 minutes. The filtration control agent is across-linked methylstyrene/acrylate copolymer and is to control fluidloss while minimizing impacts on plastic viscosity. CaCl₂ was added tothis mixture in an amount of 29.6 ppb and water in an amount of 85.3ppb, followed by mixing for 5 minutes. Barite was added to this mixturein an amount of 223.7, 223.7, 223.7, 220.7 ppb (Fluids 1-4,respectively), followed by mixing for 10 minutes. Varying amounts ofFormula 2 to this mixture were added, followed by mixing for 5 minutes.The amounts of Formula 2 for Fluids 1-4 were 0, 1.5 ppb, 1.5 ppb, and 3ppb, respectively. Each formulation was hot rolled (placed in apressurized high temperature and pressure cell and rolled at 250° F. for16 hours after all components were added to the formulation).

TABLE 2A Mixing Time Fluid after formulation component addition in orderof addition (min) Fluid 1 Fluid 2 Fluid 3 Fluid 4 Safra oil (bbl) —150.3 150.3 150.3 150.3 Emulsifier (ppb) 5 10 10 10 10 (LE SUPERMUL ™)LIME (ppb) 5 1.5 1.5 1.5 1.5 Rheology Agent—C36 5 1.5 0 1.5 1.5 fattydimer diacid (ppb) Filtration Control Agent 5 2 2 2 2 (ppb) (ADAPTA ®)CaCl₂ (ppb) 5 29.6 29.6 29.6 29.6 Water (ppb) 85.3 85.3 85.3 85.3 Barite(ppb) 10 223.7 222.7 220.7 220.7 Rheology Agent—C36 5 0 1.5 1.5 3 fattydimer diamine (ppb)

Each of the four IEFs of Table 2A were tested in a standard oilfieldviscometer at 3, 6, 100, 200, 300, and 600 rpm, and further were testedfor gel strength and HTHP fluid loss. Gel Strength test and the HTHPfluid loss test were performed as described previously for the firstexample set of IEFs. From the test data, PV, YP, and LSYP werecalculated and are shown in Table 2B for the four fluids of Table 2A.

TABLE 2B Test Fluid 1 Fluid 2 Fluid 3 Fluid 4 600 rpm (cP) 36 34 49 74300 rpm (cP) 23 20 36 52 200 rpm (cP) 19 14 29 43 100 rpm (cP) 13 9 2131  6 rpm (cP) 4 1 9 10  3 rpm (cP) 3 1 8 9 PV (lbf/100 ft²) 13 14 13 22YP (lbf/100 ft²) 10 6 23 30 LSYP (lbf/100 ft²) 2 1 7 8 Gel Strength—10sec, 5.1 1.9 7 10 (lbf/100 ft²) Gel Strength—10 min, 3.6 2.6 9 12(lbf/100 ft²) HTHP fluid loss—250° F., 6 2 2 2 500 psi, 30 min (mL)

FIG. 2 graphically illustrates PV, YP, and LSYP data of the four fluidsof Table 2A, in accordance with various embodiments. As can be seen inTable 2B and in FIG. 2, the YP values for Fluids 1 and 2 are lesser incomparison to the YP values for Fluids 3 and 4 (10 and 6 versus 23 and30, respectively). Additionally, the LSYP values for Fluids 1 and 2 aresignificantly lesser than the threshold of 7 lbf/100 ft² (1 and 4) incontrast to values of 7 and 8 lbf/100 ft² for Fluids 3 and 4. As Fluid 1contains Formula 1 but no Formula 2, and Fluid 2 contains Formula 2 butno Formula 1, Formula 1 and Formula 2 used alone as rheology modifiersare inadequate. In contrast, when both Formula 1 and Formula 2 are addedto a formulation as shown for Fluids 3 and 4, there is a synergistic andlarge impact upon YP and LSYP, jumping from values of 6-10 to values of23-30 for YP and from values of 1-2 to values of 7-8 for LSYP. Thisresult is disproportionate to the dosages as the dosages for Fluid 3 isthe same for Fluid 1 and Fluid 2, namely, 1.5 ppb of both Formula 1 andFormula 2. The doubling of Formula 2 from 1.5 ppb to 3 ppb for Fluid 4further increases YP and LSYP; however, the values may have plateauedfor LSYP as the increase is only from 7 to 8 for LSYP. Notably, the PVvalue of Fluid 3 is about the same as for Fluids 1 and 2. In summary,this data shows that Formula 1 combined with Formula 2 improves fluidrheology disproportionately and unexpectedly for drilling fluidpurposes, indicating a synergism between the two rheology modifiers.

In a third example set of IEFs, a C16-C18 fatty acid and Formula 2 wereused as a rheology modifier combination to formulate various 90 pcf IEFsthat are substantially free of organoclay. The C18 portion of the fattyacid has the chemical structure shown in Formula 3. The C16 portion ofthe fatty acid has two less carbons in the linear chain as compared toFormula 3.

Table 3A provides formulation data for three IEFs with different amountsof Formula 2 and Formula 3. The formulations are labeled as Fluids 1-3.For the formulation of Fluids 1-3, 146.7, 144.4, and 144.3 barrels of amineral oil (available from Safra Company Limited, headquartered inJeddah, Saudi Arabia) was added to a mixing tank, respectively. Aninvert emulsifier (LE SUPERMUL™) in an amount of 10 ppb was added to themineral oil, followed by mixing for 5 minutes. Lime in an amount of 1.5ppb was added to the mixture, followed by mixing for 5 minutes. Varyingamounts of Formula 3 were added to the mixture, followed by mixing for 5minutes. The amounts of Formula 3 for Fluids 1-3 were 0, 4.5 ppb, and 3ppb, respectively. A filtration control agent (ADAPTA®) in an amount of2 ppb was added to the mixture, followed by mixing for 5 minutes. Thefiltration control agent is a cross-linked methylstyrene/acrylatecopolymer and is to control fluid loss while minimizing impacts onplastic viscosity. CaCl₂ in varying amounts of 29.5 ppb, 29.5 ppb, and29.6 ppb (for Fluids 1-3, respectively), and water, in an amount of 84.9ppb, 84.9 ppb, and 85.3 ppb (for Fluids 1-3, respectively), were addedto the mixture, followed by mixing for 5 minutes. Barite in an amount of229.5 ppb, 228.9 ppb, and 228.9 ppb (for Fluids 1-3, respectively) wasadded to the mixture, followed by mixing for 10 minutes. Varying amountsof Formula 2 were added to the mixture, followed by mixing for 5minutes. The amounts of Formula 2 for Fluids 1-3 were 1.5 ppb, 0, and1.5 ppb, respectively. Each formulation was hot rolled, which includedplacing the mixture in a pressurized high temperature and pressure celland rolled at 250° F. for 16 hours after all components were added tothe formulation).

TABLE 3A Fluid Mixing Time formulation component after addition in orderof addition (min) Fluid 1 Fluid 2 Fluid 3 Safra oil (bbl) — 146.7 144.4144.3 Emulsifier (ppb) 5 10 10 10 (LE SUPERMUL ™) LIME (ppb) 5 1.5 1.51.5 Rheology Agent—C16-C18 5 0 4.5 3 fatty acid (ppb) Filtration ControlAgent (ppb) 5 2 2 2 (ADAPTA ®) CaCl₂ (ppb) 5 29.5 29.5 29.6 Water (ppb)84.9 84.9 85.3 Barite (ppb) 10 229.5 228.9 228.9 Rheology Agent—C36fatty 5 1.5 0 1.5 dimer diamine (ppb)

Each of the three IEFs of was added to the mixture were tested in astandard oilfield viscometer at 3, 6, 100, 200, 300, and 600 rpm, andfurther were tested for Gel Strength and HTHP fluid loss. Gel Strengthtest used and the HTHP fluid loss test were the same as for the firstset of examples. From the test data, PV, YP, and LSYP were calculatedand are shown in Table 3B for the four fluids of Table 3A.

TABLE 3B Test Fluid 1 Fluid 2 Fluid 3 600 rpm (cP) 34 65 62 300 rpm (cP)20 38 44 200 rpm (cP) 14 27 36 100 rpm (cP) 9 18 26  6 rpm (cP) 1 6 13 3 rpm (cP) 1 5 11 PV (lbf/100 ft²) 14 27 18 YP (lbf/100 ft²) 6 11 26LSYP (lbf/100 ft²) 1 4 9 Gel Strength—10 sec, 1.9 5 14 (lbf/100 ft²) GelStrength—10 min, 2.6 6 19 (lbf/100 ft²) HTHP fluid loss—250° F., 4 6 4500 psi, 30 min (mL)

FIG. 3 graphically illustrates the PV, YP, and LSYP data of the fourfluids of Table 3A, in accordance with various embodiments. As can beseen in Table 3B and in FIG. 3, the YP values for Fluid 1 and 2 are lowin comparison to the YP value for Fluid 3 (6 and 11 versus 26).Additionally, the LSYP values for Fluid 1 and Fluid 2 are significantlylesser the threshold of 7 lbf/100 ft² (1 and 4) in contrast to the valueof 9 lbf/100 ft² for Fluid 3. As Fluid 1 contains Formula 2 (diamine,1.5 ppb) but no Formula 3 (fatty acid) and Fluid 2 contains Formula 3(fatty acid, 4.5 ppb) but no Formula 2 (diamine), Formula 3 and Formula2 used alone as rheology modifiers are inadequate for the formulationsof Fluids 1 and 2. In contrast, when both Formula 3 and Formula 2 areadded to a formulation as shown for Fluid 3, there is a synergistic andlarge impact upon YP and LSYP. YP jumps from values of 6 and 11 to avalue of 26. LSYP jumps from values of 1 and 4 to value of 9. Theseresults are disproportionate to the dosages as the dosage of Formula 3for Fluid 3 is less than Fluid 2 and the dosage of Formula 2 for Fluid 3is the same as for Fluid 1. Accordingly, Formula 3 combined with Formula2 improves fluid rheology disproportionately and unexpectedly fordrilling fluid purposes, indicating a synergism between the two rheologymodifiers.

Ranges may be expressed herein as from about one particular value and toabout another particular value. When such a range is expressed, it is tobe understood that another embodiment is from the one particular valueand/or to the other particular value, along with all combinations withinsaid range. Where the range of values is described or referenced herein,the interval encompasses each intervening value between the upper limitand the lower limit as well as the upper limit and the lower limit andincludes smaller ranges of the interval subject to any specificexclusion provided.

Where a method comprising two or more defined steps is recited orreferenced herein, the defined steps can be carried out in any order orsimultaneously except where the context excludes that possibility.

While various embodiments have been described in detail for the purposeof illustration, they are not to be construed as limiting, but areintended to cover all the changes and modifications within the spiritand scope thereof.

What is claimed is:
 1. An invert emulsion drilling fluid, comprising: awater in oil emulsion; an invert emulsifier to stabilize the water inoil emulsion in an amount operable to stabilize the water in oilemulsion; a fatty acid having at least eight carbons and at least onecarboxylic acid group; a 36 carbon fatty dimer diamine; a filtrationcontrol agent; and an inorganic mineral including one or more of lime,calcium chloride, and barite.
 2. The fluid of claim 1, wherein the fattyacid is a carbon dimer diacid having the formula


3. The fluid of claim 1, wherein the 36 carbon fatty dimer diamine hasthe formula


4. The fluid of claim 1, wherein the fatty acid is a mixture of C16 andC18 saturated linear alpha carboxylic acids.
 5. The fluid of claim 1,wherein the fluid is formulated to have an oil to water ratio from 5:95to 95:5 by volume.
 6. The fluid of claim 1, wherein the fluid isformulated to have a density ranging from 63 to 164 lbm/ft³.
 7. Thefluid of claim 1, wherein the fluid is formulated without clay andwithout low gravity solids.
 8. The fluid of claim 1, wherein the fluidis formulated to have a calcium chloride (CaCl₂) water phase salinityconcentration of 200 to 390 thousand parts per million.
 9. The fluid ofclaim 1, wherein the fluid is formulated to have the invert emulsifierin an amount of 2 to 25 lbm/bbl.
 10. The fluid of claim 1, wherein thefluid is formulated to have the lime in an amount of 0.5 to 5 lbm/bbl.11. The fluid of claim 1, wherein the fluid is formulated to have the 36carbon dimer diacid in an amount of at least 0.5 to 5 lbm/bbl.
 12. Thefluid of claim 1, wherein the fluid is formulated to have the filtrationcontrol agent in an amount of 0.25 to 5 lbm/bbl.
 13. The fluid of claim1, wherein the fluid is formulated to have the 36 carbon fatty dimerdiamine in an amount of at least 0.25 lbm/bbl.
 14. The fluid of claim 1,wherein the oil is selected from the group consisting of mineral oil,diesel fuel, and synthetic oil, and combinations thereof.
 15. The fluidof claim 1, wherein the fluid is formulated to have a yield pointgreater than 15 lbf/100 ft².
 16. The fluid of claim 1, wherein the fluidis formulated to have a low shear yield point greater than 7 lbf/100ft².
 17. A method of drilling a wellbore with an invert emulsion fluid,comprising: drilling in a formation using an invert emulsion fluid,wherein the fluid includes a water in oil emulsion; an invert emulsifierto stabilize the water in oil emulsion in an amount operable tostabilize the water in oil emulsion; a fatty acid having at least eightcarbons and at least one carboxylic acid group; a 36 carbon fatty dimerdiamine; a filtration control agent; and an inorganic mineral includingone or more of lime, calcium chloride, and barite.
 18. The method ofclaim 17, wherein the fatty acid is a 36 carbon dimer diacid having theformula


19. The method of claim 17, wherein the 36 carbon fatty dimer diaminehas the formula


20. The method of claim 17, wherein the fatty acid has at least eightcarbons and at least one carboxylic acid group.
 21. The method of claim17, wherein the fatty acid is a mixture of C16 and C18 saturated linearalpha carboxylic acids.
 22. The method of claim 17, wherein the fluidhas an oil to water ratio from 5:95 to 95:5 by volume.
 23. The method ofclaim 17, wherein the fluid has a density of 63 to 164 lbm/ft³.
 24. Themethod of claim 17, wherein the fluid has a calcium chloride (CaCl₂)water phase salinity concentration of 200 to 390 thousand parts permillion.
 25. The method of claim 17, wherein the fluid has the invertemulsifier in an amount of 2 to 25 lbm/bbl.
 26. The method of claim 17,wherein the fluid has the lime in an amount of 0.5 to 5 lbm/bbl.
 27. Themethod of claim 17, wherein the fluid has the 36 carbon dimer diacid inan amount of at least 0.5 to 5 lbm/bbl.
 28. The method of claim 17,wherein the fluid has the filtration control agent in an amount of 0.25to 5 lbm/bbl.
 29. The method of claim 17, wherein the fluid has at least0.25 lbm/bbl of the 36 carbon fatty dimer diamine.
 30. The method ofclaim 17, wherein the oil is selected from the group consisting ofmineral oil, diesel fuel, and synthetic oil, and combinations thereof.31. The method of claim 17, wherein the fluid has a yield point greaterthan 15 lbf/100 ft².
 32. The method of claim 17, wherein the fluid has alow shear yield point greater than 7 lbf/100 ft².